Halt at Muhassab is not something (significant from the point of view of the Shari'ah). It is a place of halt where Allah's Messenger (way peace be upon him) halted.
Sahih Muslim Book 15, Hadith 376
← Previous Hadith Allah's Messenger (ﷺ) halted there, for it is a place from where it was easy to depart.

Sahih Muslim Book 15, Hadith 375 Next Hadith → Allah's Messenger (ﷺ) did not command me to observe halt at al-Abtah when be departed from Mina, but I came and set up his (the Holy Prcphet's) tent (of my own accord) ; and he (Allah's Apostle) came and observed halt. This hadith is narrated through another chain of transmitters from Abu Rafi' who was (in charge) of the luggage of Allah's Apostle (ﷺ).

Sahih Muslim Book 15, Hadith 377